DC bias in plasma process

ABSTRACT

Embodiments described herein relate to plasma processes. A plasma process includes generating a plasma containing negatively charged oxygen ions. A substrate is exposed to the plasma. The substrate is disposed on a pedestal while being exposed to the plasma. While exposing the substrate to the plasma, a negative direct current (DC) bias voltage is applied to the pedestal to repel the negatively charged oxygen ions from the substrate.

CROSS-REFERENCE TO RELATED APPLICATION & PRIORITY CLAIM

This application is a continuation of U.S. patent application Ser. No.16/17,530, filed Nov. 1, 2018, now U.S. Pat. No. 11,404,245, whichclaims the benefit of and priority to U.S. Provisional PatentApplication No. 62/636,669, filed Feb. 28, 2018, each is incorporated byreference herein in its entirety for all purposes.

BACKGROUND

Plasma processing has become ubiquitous in semiconductor processing. Aplasma can have various effects on gases used in processing to achieveadvantageous results. For examples, increased energies of a gas used ina plasma can permit processing at lower temperatures. Other benefits canbe achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a simplified tool, in accordance with someembodiments.

FIG. 2 illustrates an example method for applying a direct current (DC)bias to a pedestal during a plasma process, in accordance with someembodiments.

FIG. 3 is an example method for oxidizing a material on a substrate, inaccordance with some embodiments.

FIG. 4 illustrates the oxidation mechanism for silicon (Si) to formsilicon oxide (SiO₂), in accordance with some embodiments.

FIG. 5 is an example method for reducing or preventing oxidization of amaterial of a substrate during a plasma process, in accordance with someembodiments.

FIG. 6 illustrates the mechanism for reducing or preventing oxidation ofsilicon (Si), in accordance with some embodiments.

FIG. 7 is an example method for reducing fluorination of a material of asubstrate during a plasma process, in accordance with some embodiments.

FIG. 8 illustrates the mechanism for reducing fluorination of ametallization (e.g., AlCu) on the substrate, in accordance with someembodiments.

FIG. 9 is an example method for reducing oxidation and fluorination of amaterial of a substrate during a plasma process, in accordance with someembodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Embodiments described herein relate to plasma processes used insemiconductor processing. Embodiments specifically described herein arein the context of using a tunable direct current (DC) bias during aplasma process. A plasma etch process can include flowing a gas,igniting the gas to form a plasma, introducing the plasma in a chambercontaining a substrate, and using the tunable DC bias to repel orattract ions to/from the substrate.

Those skilled in the art should recognize that a full process forforming a semiconductor device and the associated structures are notillustrated in the drawings or described herein. Although variousoperations are illustrated in the drawings and described herein, nolimitation regarding the order of such steps or the presence or absenceof intervening steps is implied. Operations depicted or described assequential are, unless explicitly specified, merely done so for purposesof explanation without precluding the possibility that the respectivesteps are actually performed in concurrent or overlapping manner, atleast partially, if not entirely.

Plasma processing can be performed in semiconductor processing. A plasmais an at least partially ionized gas with positive and negativeparticles including radicals, positively and/or negatively charged ions,and electrons (negatively charged). Some examples of plasma processinginclude plasma etching and plasma ashing.

Plasma ashing may be the process of removing a photoresist (e.g., alight sensitive coating) from an etched substrate. Using a plasmasource, a monatomic (e.g., single atom) substance known as a reactivespecies can be generated. Some examples of reactive species includeoxygen, hydrogen, fluorine, or combinations thereof. The reactivespecies can be combined with the photoresist to form ash which isremoved, e.g., with a vacuum pump. High temperature ashing, orstripping, is performed to remove as much photoresist as possible, whilea “descum” process is used to remove residual photo resist in, e.g.,trenches. The two processes may use different temperatures that thesubstrate is exposed to while in the ashing chamber.

Plasma etching is a form of plasma processing that directs a plasma toetch a material. The plasma source uses an etch species of charged ions,radicals, and/or neutral atoms. Elements of the material and thereactive species in the plasma chemically react to etch the material.

While plasma ashing and plasma etching processes use radicals for theashing or etching, respectively, ions and electrons are also generated.Some plasma processes use a remote plasma in which the plasma source isremote from a location where the plasma and material interaction occurs.Remote plasma tools can diminish energy of downstream (e.g., from theplasma source downstream to the where the material is located, such asthe substrate) radicals and ions in the plasma. Some of the ions andelectrons can recombine downstream while the radicals survive; however,some ions and electrons remain in the plasma. For example, monatomicoxygen is electrically neutral and, although it does recombinedownstream during the channeling, it recombines at a slower rate thanthe positively or negatively charged free radicals, which attract oneanother. This means that when all of the free radicals have recombined,there is still a portion of the active species. Thus, after ashing thephotoresist, the exposed metal film underneath can become oxidized bythe oxygen ions. Hence, the remote plasma process can introduce ionsthat may penetrate the substrate surface. Surface modification cancreate halogen induced defects. As geometry sizes of semiconductordevices decrease, the effects of the surface modification can have agreat impact on the performance.

FIG. 1 illustrates a simplified tool 10 in accordance with someembodiments. The tool 10 includes a plasma generator 12. In someexamples, the plasma generator 12 is an inductively coupled plasma (ICP)generator or other suitable plasma generator that is operable togenerate a remote plasma 14. The remote plasma 14 is remote from the lowion region 36 in which particle interaction occurs. The plasma generator12 is powered by a power source 16. In some examples, the power source16 is a radio frequency (RF) power source (e.g., about 13.56 MHz orother suitable RF) or a microwave (MW) power source. The power source 16is grounded to a ground 18. In some examples, ultra-violet (UV) light(e.g., about 10 nm to 400 nm in wavelength) is generated in the remoteplasma 14. For example, the UV light is generated by interactions of theparticles in the remote plasma 14, resulting in photon emissions.

The tool 10 includes a pedestal 20 by which a substrate 22 (e.g., awafer) is supported during processing in the tool 10. In some examples,the substrate 22 is or includes a bulk semiconductor substrate, asemiconductor-on-insulator (SOI) substrate, or the like, that can bedoped (e.g., with a p-type or an n-type dopant) or can be undoped. Insome embodiments, the semiconductor material of the substrate 22includes an elemental semiconductor including silicon (Si) or germanium(Ge); a compound semiconductor; an alloy semiconductor; or combinationsthereof. Various integrated circuits can be formed on and/or in thesubstrate 22. The integrated circuits may include, for example,transistors (such as fin field effect transistors (FinFETs), planarFETs, or other transistors) and/or other devices on the substrate,metallizations on the substrate 22 to interconnect devices, etc. Thepedestal 20 is electrically coupled to a bias source 24. In someexamples, the bias source 24 is a direct current (DC) voltage sourcethat is grounded to the ground 18. In some examples, the bias source 24is a tunable bias source. In some examples, the bias source 24 istunable to both negative DC biases and positive DC biases. For example,the bias source 24 is tunable from about −50 V to about +50 V. The DCbias source 24 includes a pulsing function for reducing the loadingeffect between an isolated and dense pattern. The pulsing function maybe an on/off function for the DC bias source. For example, the pulsingfunction can be a square wave pulse function with any appropriate pulseduration and duty cycle. In some embodiments, the pedestal 20 includes aheating element 28 that is operable to heat the substrate 22 that isbeing supported by the pedestal 20 during processing in the tool 10. Forexample, the heating element 28 causes the substrate 22 to be heated ator to a temperature in a range from about 90° C. to about 330° C. Insome examples, the pressure may vary based on the particular process.For example, a higher temperature may be used for photoresist strippingdue to a higher etch rate, and lower temperature (e.g., less than 100°C.) may be applied after the lithography process to remove the scum ofphotoresist in the bottom of trench pattern or hole pattern. Lowertemperatures may be used in some surface treatment applications to avoidthe collapse of small line pattern with high aspect ratio due totemperature induced thermal stress as the wafer is cooled from hightemperature to room temperature.

A gas distribution plate (GDP) 30 is disposed in the tool 10 between theplasma generator 12 and the pedestal 20. The GDP 30 is grounded to theground 18. In some examples, the GDP 30 is an aluminum plate or othersuitable material. A gap 34 is between the GDP 30 and the pedestal 20.In some examples, a size of the gap 34 is adjustable. For example,placement of the pedestal 20 relative to the GD 30 is adjustable toincrease or decrease the size of the gap 34. In some examples, atranslation mechanism can be mechanically coupled to the pedestal 20 tomove the pedestal 20 farther away from or closer to the GDP 30 toincrease or decrease the size of the gap 34, respectively. In someexamples, the size of the gap 34 between the pedestal 20 and the GDP 30is in range from about 1 inch to about 3 inches. The GDP 30 distributesa gas, radicals, ions, etc. from the remote plasma 14 into a low ionregion 36. For example, the GDP 30 distributes the gas radicals, ions,etc. from the remote plasma 14 uniformly into the low ion region 36. Insome examples, the GDP 30 distributes, in the low ion region 36, UVlight from the remote plasma 14, and the low ion region 36 may furtherbe a low UV light region. The low ion region 36 may refer to a regionhaving a lower energy relative to the plasma generator 12 region. Forexample, due to the GDP 30, the UV light and/or the concentration ofions in the low ion region 36 may be lower than in the plasma generator12. The GDP 30 can have a number (e.g., a plurality) of through-holes.In some examples, the through-holes are of different or various sizes tosuppress ions of the remote plasma 14 and/or UV light. Because the GDP30 is grounded, most UV light is repelled from the surface of the GDP30.

During processing, a gas 40 is flowed into the plasma generator 12. Thegas may be delivered from a gas supply, such as a tank, to the plasmagenerator 12. In some examples, the gas may be delivered via a pipe ortube, of a suitable material such as steel, from the supply to theplasma generator 12. In some examples, the gas 40 is flowed into theplasma generator 12 at a flow rate in a range from about 200 sccm toabout 9000 sccm. In some examples, the flow rate may vary depending onthe plasma source and/or the particular process. For example, a lowerflow rate may be used for a Toroidal plasma source (e.g., around 400KHz) in a surface treatment application. A surface treatment applicationmay remove a small amount of material, such as silicon, from a surface,similar to a gentle etch process. On the other hand, a higher flow ratemay be used for an ICP plasma source, which may provide improveduniformity of photoresist stripping, or for a surface treatment. Thehigher flow rate may avoid failure of plasma ignition.

In some examples, the gas 40 includes O₂, N₂, H₂, He, Ar, CF₄, NF₃,C_(x)H_(y)F_(z), or a mixture of some or all of these gases. In someparticular examples, the gas 40 includes O₂, H₂, or a combinationthereof. The gas 40 is ignited in the plasma generator 12 to generatethe remote plasma 14. In some examples, the gas 40 is ignited via radiofrequency (RF) power (e.g., around 17.56 MHz). In some examples, the gas40 is ignited by an inductively coupled plasma (ICP) plasma source inwhich the energy is supplied by electric currents produced byelectromagnetic induction using time varying magnetic fields. The remoteplasma 14 includes plasma effluents, such as ionized, excited, and/orneutral species of the gas 40. In some examples, UV light is alsogenerated in the remote plasma 14. In some examples, a pressure in thelow ion region 36 is in a range from 0.1 Torr to about 4 Torr. In someexamples, the pressure may vary depending on the plasma source and/orthe particular process. For example, a lower pressure may be used for aToroidal plasma source in a surface treatment application. On the otherhand, a higher pressure may be used for an ICP plasma source, in aphotoresist stripping or surface treatment application. The higherpressure may avoid failure of plasma ignition. In some examples, ashrates and uniformity may be correlated to pressure, power, and flowrate. For example, 1 Torr pressure, 5000 W power, and 5000 sccm flowrate may provide high ash rates as compared to lower pressure, power,and/or flow rates.

Ionized, excited, and/or neutral species of the gas 40 from the remoteplasma 14 diffuse through the GDP 30 to the low ion region 36, where thesubstrate 22 is exposed to the ionized, excited, and/or neutral speciesof the gas 40. In some examples, the ionized, excited, and/or neutralspecies of the gas 40 and/or other ions removed from the substrate 22 ormaterial on the substrate 22 can be pumped out or removed from the tool10 by an exhaust 42.

During the exposure of the substrate 22 to the ionized, excited, and/orneutral species of the gas 40, the bias source 24 can bias the pedestal20 and hence, the substrate 22, with a DC bias voltage, to achieve adesired effect. A polarity of the DC bias voltage, a magnitude of the DCbias voltage, a pulsing function (e.g., including a duty cycle), and/orcombinations thereof may result in the desired effect, which can accountfor a loading effect between an isolated pattern and/or dense pattern.Some examples are described below to illustrate some desired effects.

FIG. 1 as described herein and illustrated in the figures is simplifiedto not obscure various aspects of the examples described herein. Aperson having ordinary skill in the art will readily understand variousmodifications of the simplified tool and/or other features that can beincorporated with the tool.

FIG. 2 is an example method for applying DC bias during a plasmaprocess, for example, to attract or repel ions to/from the substrate 22.The plasma process 200 is a general example of applying a DC bias duringplasma processing, which may be performed as a part of a semiconductordevice manufacturing process. More specific manufacturing processes andplasma processes are described below, for example, with respect to FIGS.3, 5, 7, and 9 . In block 210, a gas is flowed into a remote plasmaregion of the tool 10 as the gas 40. In some examples, the gas 40 isflowed into the plasma generator 12 at a flow rate in a range from about200 sccm to about 9000 sccm. Various gases can be flowed depending onthe plasma process being performed. As described in more detail belowwith respect to FIGS. 3 and 4 , the gas 40 could be oxygen for anoxidation process. As described in more detail below with respect toFIGS. 3 through 9 , the gas 40 could be oxygen, hydrogen, or acombination thereof, for a plasma ashing process. In some examples, thegas 40 is a fluorine-containing gas for a plasma etch process. Othergases or plasma processes can also be performed.

In block 212, the pedestal 20 is biased with a DC bias voltage. Forexample, the bias source 24 is tunable from about −50 V to about +50 V.As described in further detail below, the DC bias voltage is applied toattract or repel ions to/from the substrate 22. For example, the DC biascan be applied to oxidize, antioxidate, or defluorinate the substrate22. In some examples, the DC bias voltage is tunable, for example, toprovide a stronger or weaker attraction or repulsion of the ions and/orto switch from a negative DC bias voltage to a positive DC bias voltage,or from a positive DC bias voltage to a negative DC bias voltage.

In block 214, the gas 40 is ignited to generate the remote plasma 14.The gas 40 can be ignited before the pedestal 20 is biased with the DCbias voltage in block 212, after the pedestal 20 is biased with the DCbias voltage in block 212, or at the same time that the pedestal 20 isbiased with the DC bias voltage in block 212. In block 216, the remoteplasma 14 is then introduced to expose the substrate 22 to the plasma.For example, the remote plasma 14 is diffused through the GDP 30 to thelow ion region 36 where the substrate 22 is exposed. In some examples, apressure in the low ion region 36 is in a range from 0.1 Torr to about 4Torr. In some examples, the heating element 28 causes the substrate 22to be heated at or to a temperature in a range from about 90° C. toabout 330° C.

In a first example of the method for applying DC bias during a plasmaprocess, a remote plasma process is implemented to oxidize a material ofthe substrate 22. FIG. 3 is an example of the method for oxidizing amaterial on the substrate 22. In block 302, a layer is formed on asubstrate 22. In block 304, a process is formed to oxidize at least aportion of the layer. In other examples, the substrate 22 may beoxidized, for example, without first forming the layer at 302. In block306, an oxygen-containing gas, such as O₂, is flowed into a remoteplasma region in the tool 10 as the gas 40. In some examples, theoxygen-containing gas is flowed into the plasma generator 12 at a flowrate in a range from about 200 sccm to about 9000 sccm. In block 308,the pedestal 20 is biased with a positive DC bias voltage applied to thepedestal 20 to attract negative oxygen ions. In some examples, the DCbias is tunable. For example, the bias source 24 is tunable from about+1 V to about +50 V. A larger positive bias can be used to form athicker oxide layer and a smaller positive bias can be used to form athinner oxide layer. In block 310, the oxygen-containing gas is ignitedto form the remote plasma 14. The ignition of the oxygen-containing gasat block 310 to generate the remote plasma 14 can be before the pedestal20 is biased with the DC bias voltage at block 308, after the pedestal20 is biased with the DC bias voltage at block 308, or at the same timethat the pedestal 20 is biased with the DC bias voltage at block 308.Next, in block 312, the remote plasma 14 is introduced to the substrate22 to expose the substrate 22 to the plasma. For example, the remoteplasma 14 is diffused through the GDP 30 to the low ion region 36 wherethe substrate 22 is exposed. In some examples, a pressure in the low ionregion 36 is in a range from 0.1 Torr to about 4 Torr. In some examples,the heating element 28 causes the substrate 22 to be heated at or to atemperature in a range from about 90° C. to about 330° C. For example,for an oxidation process, temperatures higher than 200° C. may bepreferred.

Further processing steps may be included in the manufacturing process ofthe semiconductor device. In block 314, a photoresist may be depositedon the oxidized layer. In block 316, the photoresist is patterned. Thepatterning may depend on the lithography process and type of photoresistbeing used. The patterning may include masking and exposure to light forexample. In block 318, additional processing of the substrate 22 may beperformed, such as an etch process using the patterned photoresist.

FIG. 4 illustrates the oxidation mechanism for silicon (Si) to formsilicon oxide (SiO₂) as an example. In other examples silicon germanium(SiGe) or other materials can be oxidized with the process of FIG. 3 .Oxidation mechanisms include thermal oxidation and plasma oxidation.Thermal oxidation can involve a high activity energy (e.g., around 2 eV)and a neutral oxygen species. Plasma oxidation can involve a lowactivation energy (e.g., around 0.15 eV) and negative oxygen ions. Theremote plasma generated by igniting the oxygen-containing gas at block310 contains negative oxygen ions (e.g., O²⁻ and O⁻). The negativeoxygen ions then become exposed to the substrate 22 in the low ionregion 36. The positive DC bias voltage from the bias source 24 that isapplied at block 308 causes a positive electrical charge to accumulateon the pedestal 20 at the surface that supports the substrate 22. Thepositive electrical charge on the surface of the pedestal 20 can cause apositive charge to accumulate on the surface of the substrate 22 distalfrom the pedestal 20. Because the oxygen ions are negatively charged andthe surface of the substrate 22 distal from the pedestal 20 ispositively charged, an electrostatic force (e.g., attraction) existsbetween the negative oxygen ions and the substrate 22. The electrostaticforce (e.g., attraction) between the negative oxygen ions and thepositive charge on the pedestal 20 can cause the oxygen ions topenetrate into the substrate 22, which permits the oxygen ions to reactwith a material, e.g., silicon, of the substrate 22 to oxidize thematerial. A larger positive DC bias voltage and/or larger duty cycle canresult in a higher oxidation rate, more oxidation, and a thicker oxidelayer. In some examples, more oxidation is implemented, such as for anitride film oxidation, to improve photoresist adhesion and profile,control fin width, increase metal oxidation of isolation, etc. In someexamples, the rate of oxidation is a function of the oxygen flow rate,the amplitude of the positive DC bias applied, a duration of theprocess, electron density in the plasma, and/or other factors such astemperature. In some examples, the DC bias voltage is applied to controla uniformity of the oxidation of the substrate 22 material.

In a second example of the method for applying DC bias during a plasmaprocess, a remote plasma process can be implemented to reduce or preventoxidization of a material of the substrate, such as during an ashingprocess. FIG. 5 is an example method for reducing or preventingoxidization of a material of the substrate during a plasma process. Inblock 502 a layer may be formed on a substrate, such as the substrate22. In block 504, a photoresist may be deposited on the layer. In block506, the photoresist is patterned. In some examples, the photoresist maybe deposited on the substrate 22, for example, rather than forming thelayer in block 502. In block 507, additional processing may be performedafter patterning the photoresist, for example, an etch process could beperformed. In block 508, a process is performed to remove thephotoresist, including the blocks 512-517. In block 512, anoxygen-containing gas (and/or a nitrogen-containing gas), such as O₂, isflowed into a remote plasma region of the tool 10 as the gas 40. someexamples, the oxygen-containing gas is flowed into the plasma generator12 at a flow rate in a range from about 200 sccm to about 9000 sccm. Theoxygen-containing gas can be used in an ashing process to remove variouslayers, such as the photoresist or a bi-layer or tri-layer structureused for patterning the deposited layer and/or substrate 22. In block514, the pedestal 20 is biased with a negative DC bias voltage to repelthe negative oxygen ions. In block 516, the oxygen-containing gas isignited to generate the remote plasma 14 for the plasma process. In someexamples, the DC bias voltage is tunable. For example, the bias source24 is tunable from about −1 V to about −50 V. A larger negative DC biascan be used to further reduce or eliminate oxidation during the plasmaprocess. The ignition of the oxygen-containing gas at block 516 togenerate the remote plasma 14 can be before the pedestal 20 is biasedwith the negative DC bias voltage at block 514, after the pedestal 20 isbiased with the negative DC bias voltage at block 514, or at the sametime that the pedestal 20 is biased with the negative DC bias voltage atblock 514. Next, in block 517, the remote plasma 14 is introduced to thesubstrate 22 to expose the substrate 22 to the plasma. For example, theremote plasma 14 is diffused through the GDP 30 to the low ion region 36where the substrate 22 is exposed. In some examples, a pressure in thelow ion region 36 is in a range from 0.1 Torr to about 4 Torr. In someexamples, the heating element 28 causes the substrate 22 to be heated ator to a temperature in a range from about 90° C. to about 330° C. In aprocess to remove photoresist, a higher temperature (e.g., higher than200° C.) may be used for a higher ash rate; but, the higher temperaturemay increase oxidation and, in turn, substrate loss. However, by usingthe negative DC bias to repel oxygen ions, the higher ash rate can stillbe achieved without increased oxidation. In block 518, additionalprocessing may be performed, such as depositing additional layers ormaterial and etching.

FIG. 6 illustrates the mechanism for reducing or preventing oxidation(e.g., antioxidation) of silicon (Si) as an example. The remote plasma14 contains negative oxygen ions (e.g., O²⁻ and O⁻) that then becomeexposed to the substrate 22 in the low ion region 36. If the oxygen ionspenetrate the silicon layer 63 of the substrate 22, the silicon layer 63can oxidize to form the SiO₂ layer 61. The negative DC bias voltage fromthe bias source 24 causes a negative electrical charge to accumulate onthe pedestal 20 at the surface that supports the substrate 22. Thenegative electrical charge on the surface of the pedestal 20 can cause anegative charge to accumulate on the surface of the substrate 22 distalfrom the pedestal 20. An electrostatic force (e.g., repulsive) iscreated by the negatively charged oxygen ions and the negative chargeaccumulated on the surface of the substrate 22 distal from the pedestal.The electrostatic force (e.g., repulsive) between the negative oxygenions and the negative charge on the surface of the substrate 22 distalfrom pedestal 20 can cause the oxygen ions to be repelled from thesubstrate 22 to thereby reduce or prevent the oxygen ions frompenetrating or coming into contact with a material, e.g., silicon layer63, of the substrate 22, which can reduce or prevent oxidization of thematerial. Substrate loss can thereby be mitigated. Thus, the ashingprocess shown in FIG. 5 can simultaneously achieve both ashing of thephotoresist with the remaining radicals (O*) and antioxidation of thematerial of the substrate 22 by repelling the negative oxygen ions(e.g., O²⁻ and O⁻).

In some examples, the oxygen ashing process and the oxidation processare performed sequentially. For example, the oxygen ashing process asdescribed with respect to FIGS. 5 and 6 can be performed to strip aphotoresist from the substrate 22 using the negative DC bias voltage toprevent or reduce oxidation during the ashing process. Next, thepositive DC bias voltage could be applied to perform the oxidationprocess as described with respect to FIGS. 3 and 4 if an oxide layer isdesired.

In a third example of the method for applying DC bias during a plasmaprocess, a remote plasma process can be implemented to reducefluorination (e.g., defluorinate) of a material of the substrate, suchas during an ashing process. In some examples, fluorination of thematerial occurs during a process prior to the ashing process and can beremoved during the ashing process. In some examples, the fluorination ofthe material occurs during an etch process. For example, an etchingprocess can implement fluorine-based gases and plasmas. In thoseexamples, negative fluorine ions can penetrate (e.g., diffuse into) amaterial of the substrate 22 causing fluorination of the material, whichcan cause defects. For example, presence of fluorine in the material ofthe substrate 22 can induce outgassing in subsequent processing of thesubstrate 22. The outgassing can lead to defects such as condensationdefects, film voids, and/or fluorinated pads leading to corrosion of thepad. In some examples, after such an etch process, an ashing processand/or an additional treatment process implementing a remote plasma isperformed. As described in FIG. 7 , the plasma process can beimplemented to reduce the fluorination of the material.

FIG. 7 is an example method for reducing fluorination of a material ofthe substrate during a plasma process. The manufacturing processillustrated in FIG. 7 involves a process that uses fluorine, such as anetch process prior to the ashing process. As shown in FIG. 7 , in block702 a layer may be formed on a substrate, such as the substrate 22. Inblock 704, a photoresist may be deposited on the layer. In block 706,the photoresist is patterned. In some examples, the photoresist may bedeposited on the substrate 22, for example, rather than forming thelayer in block 702. Additional processing may be performed afterpatterning the photoresist, for example, in block 707 a fluorine etchprocess is performed on the layer. In block 708, a process is performedto remove the photoresist, including the blocks 712-717. In block 712, ahydrogen-containing gas, such as H₂, is flowed into a remote plasmaregion in the tool 10 as the gas 40. In some examples, thehydrogen-containing gas (and sometimes also a nitrogen-containing gas)is flowed into the plasma generator 12 at a flow rate in a range fromabout 200 sccm to about 9000 sccm. The hydrogen-containing gas can beused in an ashing process to remove various layers, such as thephotoresist or a bi-layer or tri-layer structure used for patterning thedeposited layer and/or substrate 22. In block 714, the pedestal 20 isbiased with a negative DC bias voltage to repel negative fluorine ions.In some examples, the DC bias is tunable. For example, the bias source24 is tunable from about −1 V to about −50 V. A larger negative DC biasvoltage can be used to further reduce or eliminate fluoridation duringthe plasma process. In block 716, the hydrogen-containing gas is ignitedto generate the remote plasma 14 for the plasma process. The ignition ofthe hydrogen-containing gas at block 716 to generate the remote plasma14 can be before the pedestal 20 is biased with the negative DC biasvoltage at block 714, after the pedestal 20 is biased with the negativeDC bias voltage at block 714, or at the same time that the pedestal 20is biased with the negative DC bias voltage at block 714. Next, in block717, the remote plasma 14 is introduced to the substrate 22 to exposethe substrate 22 to the plasma. For example, the remote plasma 14 isdiffused through the GDP 30 to the low ion region 36 where the substrate22 is exposed. In some examples, a pressure in the low ion region 36 isin a range from 0.1 Torr to about 4 Torr. In some examples, the heatingelement 28 causes the substrate 22 to be heated at or to a temperaturein a range from about 90° C. to about 330° C. In a process to removephotoresist, a higher temperature (e.g., higher than 200° C.) may beused for a higher ash rate as well as better removal of the fluorine. Inblock 718, additional processing may be performed, such as depositingadditional layers or material and etching.

FIG. 8 illustrates the mechanism for reducing fluorination of a material(e.g., a metallization such as AlCu) on the substrate 22 as an example.A bi-layer or tri-layer structure, such as oxide layer 83, SiN layer 81,and hardmask layer 85, is implemented for masking and patterning ametallization (e.g., AlCu) layer 87 and a dielectric layer 89. Thepatterning uses a fluorine-based plasma that causes negative fluorineions (F⁻) to diffuse into the metallization layer 87. The plasmaincludes positive hydrogen ions (e.g., H⁺) that then become exposed tothe substrate 22 in the low ion region 36. The negative DC bias voltagefrom the bias source 24 causes a negative electrical charge toaccumulate on the pedestal 20 at the surface that supports the substrate22. An electrostatic force (e.g., repulsive) is created between thenegative fluorine ions and the negative charge on the pedestal 20. Theelectrostatic force between the negative fluorine ions and the negativecharge on the pedestal 20 can cause the fluorine ions to be repelled andremoved from the substrate 22 to thereby reduce fluorination of themetallization layer 87. An electrostatic force (e.g., attractive) existsbetween the positive hydrogen ions and the negative fluorine ions. Theelectrostatic force between the positive hydrogen ions and the negativefluorine ions can also further cause the negative fluorine ions to beremoved from the substrate 22 thereby reducing fluorination of themetallization layer 87. The removed fluorine atoms can be attracted toand react with the hydrogen ions to form volatile hydrofluoric acid (HF)(e.g., F⁻+H⁺→HF_(gas)), which can be pumped or exhausted 42 out of thetool 10. Thus, the ashing process shown in FIG. 7 can simultaneouslyachieve both ashing of the photoresist and defluorination of thematerial of the substrate 22.

In a fourth example of the method for applying DC bias during a plasmaprocess, a remote plasma process is implemented for anti-oxidizing andde-fluorinating a material of the substrate 22. FIG. 9 is an examplemethod that includes removing a photoresist in block 908 that furtherreduces oxidization and fluorination of a material on the substrate 22.For example, the plasma process of FIG. 9 can be implemented in themanufacturing process illustrated in FIG. 7 in which a fluorine etch isperformed in the process. In block 912, an oxygen-containing gas, suchas O₂, is flowed into a remote plasma region in the tool 10 as the gas40. In block 914, the pedestal 20 is biased with a negative DC biasvoltage. In block 916, the oxygen-containing gas is ignited to form theremote plasma 14. The ignition of the oxygen-containing gas at block 916to generate the remote plasma 14 can be before the pedestal 20 is biasedwith the negative DC bias voltage at block 914, after the pedestal 20 isbiased with the negative DC bias voltage at block 914, or at the sametime that the pedestal 20 is biased with the negative DC bias voltage atblock 914. Next, in block 918, the remote plasma 14 is introduced to thesubstrate 22 to expose the substrate 22 to the plasma. For example, theremote plasma 14 is diffused through the GDP 30 to the low ion region 36where the substrate 22 is exposed. The blocks 912-918 can be implementedas an ashing process to remove photoresist from the substrate 22. Use ofthe negative DC bias during the ashing process reduces or preventsoxidation of the material of the substrate, for example, as describedabove with respect to FIG. 6 for the example of the mechanism ofreducing or preventing oxidation of silicon by repelling the negativeoxygen ions.

The method can further be used to defluorinate the substrate 22. Forexample, prior to the ashing process of FIG. 9 , the process 707 usingfluorine can be performed, such as a plasma etch process using fluorine.The process using fluorine results in fluorination of a material on thesubstrate 22, such as a metallization. Thus, in block 920, the methodstops flowing the oxygen-containing gas, and in block 922, ahydrogen-containing gas, such as H₂, is flowed into a remote plasmaregion of the tool 10 as the gas 40. In some examples, the pedestal 20may remain biased with the negative DC bias voltage used during theoxygen ashing in block 914. In some examples, the negative DC biasvoltage could be turned off, and is turned back on. In some examples,the negative DC bias voltage can be tuned to a different negative DCbias voltage. For example, a first negative DC bias voltage may be usedduring the oxygen ashing and a different negative DC bias voltage isused during the defluorination. In block 924, the hydrogen-containinggas is ignited to form a second remote plasma 14. The second remoteplasma 14 is then introduced to the substrate 22 to expose the substrate22 to the plasma in block 926. For example, the second remote plasma 14is diffused through the GDP 30 to the low ion region 36 where thesubstrate 22 is exposed. The negative DC bias voltage causes fluorineions to leave material of the substrate 22, thereby defluorinating thematerial of the substrate 22, for example, as described above withrespect to FIG. 8 for the example of the mechanism of reducing orpreventing fluorination of AlCu. Thus, the method of FIG. 9 can providean efficient technique to achieve simultaneous defluorination andphotoresist removal, with minimal oxidation, in a single dry ashprocess.

In a fifth example of the method for applying DC bias during a plasmaprocess, a remote plasma process is implemented for anti-oxidizing andde-fluorinating a material of the substrate 22. An oxygen-containing gasand hydrogen-containing gas are flowed into the tool 10 as the gas 40and ignited to form the remote plasma 14. The pedestal 20 is biased witha negative DC bias voltage. The oxygen and/or hydrogen plasma can beused to ash the photoresist, while the negative DC bias voltage appliedto the pedestal 20 reduces or prevents oxidation and also cause fluorideto be released. The fluoride can combine with the hydrogen ions and beremoved from the tool 10 by the exhaust 42.

The example methods described herein are to illustrate aspects ofvarious embodiments. Embodiments may be implemented in and/or for otherprocesses that would be readily understood by a person having ordinaryskill in the art. Further, some aspects of the example methods describedabove can be implemented together and/or in combination with otherfeatures not described herein. For example, an ash process can implementO₂ and H₂ gas to achieve various benefits described herein. The examplemethods may also be performed in any logical order, and any orderdescribed herein or illustrated in the figures is merely for conveniencein describing the examples. Various embodiment methods may be performedin other orders.

Embodiments can have benefits. For example, some embodiments can reduceor avoid oxidation of a substrate during an ashing process. Further,substrate loss from the ashing process can be reduced or avoided.Penetration of halogenic ions into a substrate can be reduced oravoided, which can reduce or avoid defects in the substrate. Someembodiments can reduce or eliminate fluorination of a substrate duringan ashing process, which can avoid defects in the substrate. Someembodiments can reduce or avoid oxidation of a substrate and also reduceor eliminate fluorination of the substrate during a single ashingprocess. Some embodiments can increase oxidation during a plasmaprocess.

In an embodiment, a method is provided. The method includes generating aplasma containing negatively charged oxygen ions. The method includesexposing a substrate to the plasma. The substrate is disposed on apedestal while being exposed to the plasma. The method includes applyinga negative direct current (DC) bias voltage to the pedestal whileexposing the substrate to the plasma to repel the negatively chargedoxygen ions from the substrate.

In another embodiment, a method is provided. The method includesgenerating a plasma comprising positively charged hydrogen ions. Themethod includes exposing a substrate to the plasma. The substratecontains negatively charged fluorine ions and is disposed on a pedestalwhile being exposed to the plasma. The method includes applying anegative direct current (DC) bias voltage to the pedestal to repel thenegatively charged fluorine ions from the substrate while exposing thesubstrate to the plasma.

In yet another embodiment, a method is provided. The method includesgenerating a plasma containing negatively charged oxygen ions. Themethod exposing a substrate to the plasma. The substrate is disposed ona pedestal while being exposed to the plasma. The method includesapplying a positive direct current (DC) bias voltage to the pedestal toattract the negatively charged oxygen ions to the substrate whileexposing the substrate to the plasma.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: placing a substrate on apedestal within a chamber, the chamber comprising a first region and asecond region separated by a gas distribution plate, the pedestal beingdisposed within the second region of the chamber, the substratecomprising negatively charged fluorine ions; and performing a plasmaprocess on the substrate, performing the plasma process comprises:generating a plasma in the first region of the chamber, the plasmacomprising positively charged hydrogen ions and negatively chargedoxygen ions; filtering the plasma by the gas distribution plate into thesecond region of the chamber to expose the substrate to the positivelycharged hydrogen ions and the negatively charged oxygen ions; andapplying a negative direct current (DC) bias voltage to the pedestal toremove the negatively charged fluorine ions from the substrate and torepel the negatively charged oxygen ions from the substrate.
 2. Themethod of claim 1, wherein generating the plasma includes generating anultra-violet light.
 3. The method of claim 2, wherein the gasdistribution plate at least partially blocks the ultra-violet light. 4.The method of claim 1, wherein applying the negative DC current occurswhile generating and filtering the plasma.
 5. The method of claim 1,further comprising pumping hydrofluoric acid from the chamber.
 6. Themethod of claim 1, wherein applying the negative DC bias voltagecomprises pulsing the negative DC bias voltage.
 7. The method of claim1, wherein filtering the plasma exposes the substrate to neutral oxygenradicals.
 8. A method comprising: placing a substrate on a pedestalwithin a chamber, the chamber comprising a first region and a secondregion separated by a gas distribution plate, the pedestal beingdisposed within the second region of the chamber, the substratecomprising negatively charged fluorine ions; and performing a plasmaprocess on the substrate, performing the plasma process comprises:flowing a hydrogen-containing gas and an oxygen-containing gas into thefirst region of the chamber; igniting the hydrogen-containing gas andthe oxygen-containing gas to generate a plasma in the first region ofthe chamber, the plasma comprising positively charged hydrogen ions andnegatively charged oxygen ions; adjusting a distance between the gasdistribution plate and the pedestal; diffusing the plasma through thegas distribution plate into the second region of the chamber to exposethe substrate to the positively charged hydrogen ions and the negativelycharged oxygen ions; and applying a negative direct current (DC) biasvoltage to the pedestal to remove the negatively charged fluorine ionsfrom the substrate and to repel the negatively charged oxygen ions fromthe substrate.
 9. The method of claim 8, wherein igniting the plasma isperformed before applying the negative DC bias voltage.
 10. The methodof claim 8, wherein applying the negative DC bias voltage is performedprior to igniting the plasma.
 11. The method of claim 8, furthercomprising, prior to performing the plasma process: forming a layer onthe substrate; and etching the layer with a fluorine-containing gas. 12.The method of claim 8, further comprising removing HF gas from thechamber.
 13. The method of claim 8, further comprising removingnegatively charged oxygen ions from the chamber.
 14. The method of claim8, wherein the negative DC bias voltage is in a range between −1V and−50V.
 15. A method comprising: forming a layer over a substrate; forminga patterned photoresist on the layer; etching the layer with afluorine-based etchant while using the patterned photoresist as an etchmask, wherein negatively charged fluorine ions diffuse into thesubstrate; removing the patterned photoresist, wherein removing thepatterned photoresist comprises: placing the substrate on a pedestalwithin a chamber, the chamber comprising a first region and a secondregion separated by a gas distribution plate, the pedestal beingdisposed within the second region of the chamber; and generating aplasma in the first region of the chamber, the plasma comprisingpositively charged hydrogen ions and negatively charged oxygen ions;filtering the plasma by the gas distribution plate into the secondregion of the chamber to expose the substrate to the positively chargedhydrogen ions and the negatively charged oxygen ions; and applying anegative direct current (DC) bias voltage to the pedestal to remove thenegatively charged fluorine ions from the substrate and to repel thenegatively charged oxygen ions from the substrate.
 16. The method ofclaim 15, wherein the layer is a dielectric layer, and wherein thesubstrate comprises a metal layer, wherein the negatively chargedfluorine ions diffuse into the metal layer.
 17. The method of claim 16,further comprising removing hydrofluoric acid from the chamber, whereinthe hydrofluoric acid comprises the negatively charged fluorine ionsfrom the metal layer.
 18. The method of claim 15, further comprisingfiltering ultra-violet light by the gas distribution plate from thefirst region to the second region.
 19. The method of claim 15, whereingenerating the plasma comprises igniting a process gas comprising O₂ gasand H₂ gas.
 20. The method of claim 15, further comprising pulsing thenegative DC bias voltage.